Hypothenar eminence

Abstract: Pain, weakness, and sensory loss occur frequently in the hypothenar eminence. However, clinical examination is difficult and nonspecific, and the prescribed imaging technique may be inadequate, or images may be misinterpreted. Different imaging modalities have various degrees of usefulness for the diagnosis of painful pathologic conditions of the hypothenar eminence. Radiography, multidetector computed tomography (CT), multidetector CT arthrography, and magnetic resonance (MR) imaging of the wrist are useful for surveying the anatomy of the hypothenar eminence, the Guyon canal, and the ulnar nerve and artery and for determining the cause of pain or other symptoms. A fracture of the pisiform bone or the hook of the hamate bone, osteoarthritis or osteochondromatosis of the pisotriquetral joint, Guyon canal syndrome, hypothenar hammer syndrome, tendinopathy of the flexor carpi ulnaris, an anomalous muscle, a ganglion cyst, or a tumor may be responsible for ulnar neuropathy. Specific radiographic views, such as the semisupinated oblique view and the lateral view with the hand radially deviated and the thumb abducted, often provide a sufficient basis for the diagnosis of acute fracture of the hook of the hamate or the pisiform bone. Multidetector CT angiography is an efficient method for diagnosing hypothenar hammer syndrome, and multidetector CT arthrography is well suited for evaluation of the pisotriquetral joint. MR imaging is the modality of choice for depiction of the ulnar nerve.

Abstract: A concept of finger motion and control, based on electromyographic observations in 868 muscles in 256 normal, adult subjects, is presented. This concept is a logical extension of the hypothesis previously reported10. Hand control depends on active contractile forces during both lengthening and shortening of the muscles, on the viscoelastic properties of all of the tissues of the hand and forearm, especially the muscles, and on the anatomical configuration of related structures. The control mechanism can be described in terms of the contributions of the several structures during the process of reaching or holding the four common, terminal positions of the fingers. 1. The fully extended finger: To reach or hold the position of full extension of all joints, contraction of both the extrinsic and intrinsic muscles is required. The extensor digitorum and lumbricalis actively contract of provide the extending force. The lumbricalis is particularly effective in interphalangeal extension since it pulls the flexor digitorum profundus tendon distally, relieving the interphalangeal joints of the passive flexing force produced by the viscoelastic properties of the profundus. 2. The clawed finger: To reach or hold the position of interphalangeal flexion and metacarpophalangeal extension, contraction of only the extrinsic muscles is required. The flexor digitorum profundus (and to a lesser extent the flexor digitorum superficialis) and the extensor digitorum are the active muscles. 3. The fully flexed finger: To reach or hold the position of full flexion of all joints, contraction of only the extrinsic muscles is required. The active muscles are the flexor digitorum profundus (and to a lesser extent the flexor digitorum superficialis) and the extensor digitorum. The actively contracting muscles are therefore the same here as in the clawed position. The ability of the finger to use these same muscles to reach the fully flexed position depends upon: the lengthening contraction of the extensor digitorum as the finger is fully flexed permitting controlled metacarpophalangeal flexion and the increased tension in the oblique track, primarily the result of stretching of the bi-articular interossei. 4. Metacarpophalangeal flexion with the finger straight: To reach or hold the position of interphalangeal extension and metacarpophalangeal flexion, contraction of the intrinsic muscles is required, and to a lesser extent contraction of the extrinsic extensor. The motion is performed by contraction of the lumbricalis and the interossei. Of the flexion-extension motions, only those reaching or holding this position are associated with action of the interossei as a group. Activity of the extensor digitorum, a frequent accompaniment of this motion, assists interphalangeal extension and prevents hyperflexion of the metacarpophalangeal joint. The lumbricalis emerges as an extremely consistent performer in all individuals and fingers. The interossei have certain group characteristics, but vary moderately from finger to finger and from subject to subject. This paper has described these variations and presented the supporting data; lumbricoid and pure metacarpophalangeal flexor variations of interosseus behavior are noted. The flexor digitorum profundus consistently overshadows the superficialis, except in the index finger where the superficialis sometimes predominates. The extensor digitorum and the extensors proprii appear to have identical functions. The muscles of the hypothenar eminence do not contribute significantly to flexion-extension motions of the small finger, but the opponens digiti minimi may participate as a depressor of the fifth metacarpal during closing motions.

Abstract: I. Introduction. II. Development of the Hand. III. Distal Forearm, Wrist, and Palm. IV. Distal Forearm, Wrist, and Thenar Eminence. V. Thumb. VI. Distal Forearm, Wrist, and Hypothenar Eminence. VII. Palm. VIII. Distal Palm and Proximal Fingers. IX. Palmar Finger. X. Distal Forearm, Wrist, and Dorsum. XI. Dorsal Finger.

Abstract: The boundaries of the space through which the ulnar neurovascular bundle crosses the wrist have been reinvestigated. Using gross dissections, transverse and sagittal sections, and histologic study, we determined that the roof of Guyon's canal, the "carpal ulnar neurovascular space," does not directly connect to the hamate bone, as is currently accepted. The roof of this space extends radially to the hook of hamate and attaches to the flexor retinaculum. This anatomic arrangement allows the ulnar artery and sensory component of the ulnar nerve to course radially to the hook of hamate, where they lie on the flexor retinaculum (transverse carpal ligament). The roof and radial border have three segments: (1) a proximal segment that begins near the pisiform and extends distally to the level of the hook of hamate but does not attach directly to it, (2) a central segment that contains only adipose tissue, and (3) a distal fascial layer that includes the palmaris brevis muscle. The floor of the space consists of the muscles of the hypothenar eminence, their fibers of origin, and the flexor retinaculum (transverse carpal ligament). Guyon accurately described the proximal portion of the carpal ulnar neurovascular space, but his description has been misinterpreted; the hook of hamate does not serve as the radial boundary of Guyon's canal. The anatomic relationships of the "carpal ulnar neurovascular space" need to be appreciated to avoid complications during carpal tunnel surgery.